Bird flu has spread in Burma with more than 100 outbreaks across the country, a UN official has said.
Outbreaks of the virus were first reported in Mandalay in March
He Changchui of the UN's Food and Agriculture Organization (FAO) told a press conference the situation was "more serious than we imagined".
He said the outbreaks were mainly in the central district of Mandalay and the northern district of Sagaing.
On 13 March Burma confirmed its first case of H5N1 since November 2004 and the number subsequently rose to five.
Mr He, who is the FAO's Asia-Pacific representative, was speaking after two teams from the agency visited Burma to assess the situation.
He said it had not been easy to find accurate information.
"The issue there is that awareness is rather poor," he said. "The information is not that comprehensive."
He said Burma lacked scientific equipment and facilities to deal with the outbreaks and would need international assistance.
UN bird flu co-ordinator David Nabarro, who is currently visiting South East Asia, said there were major problems in Burma.
"We're going to be focusing on Myanmar [Burma] a lot in the next few days and weeks, trying to make sure that the authorities and civil society are able to cope better," he said.
On 13 March Burma told the FAO that it had detected the first outbreak of bird flu in poultry in the central town of Mandalay, 700km (450 miles) north of Rangoon.
Five thousand chickens were culled and state media warned people to report suspected infections promptly.
There have been no reported human victims of the virus in Burma. More than 100 people around the world have died from the H5N1 strain of the disease since 2003.
The vast majority of the deaths have been in Asia, but cases in people and birds have also been recorded in Europe and Africa.
Experts fear the virus could mutate into a form that passes easily between humans, possibly sparking a pandemic, but there is no evidence that this has happened yet.